West Germany will halt future exports of controversial nuclear technology that could be used to make atomic weapons but will fulfill its existing contract to supply atomic power plants and technology to Brazil, the Bonn government announced today.

The statement, coming at the close of two days of talks here between West German Chancellor Helmut Schmidt and French President Valerie Giscard d'Estaing, marks an important advance in the stepped-up efforts of industrialized countries to try to stop the spread of nuclear weapons technology.

On the surface, it would appear that the West German statment is not a major concession by the Bonn government because it does not affect the controversial $5 billion sale to Brazil - which the Carter administration has been trying to get canceled. Also, Bonn does not have any immediate customers lined up for future sales.

Nevertheless, the West German position is important for several reasons:

There are several countries, for example Iran, that could request licenses for West German nuclear fuel-reprocessing technology at any time, and the government statement now rules such sales out at least until further notice.

In previous statements, government spokesmen and Schmidt have indicated that they would refrain from future sales like that to Brazil only if others pledge to do likeswise. There is no such caveat in today's statement.

Finally, Boon's acknowledgement that "the Federal Republic of Germany will . . . until futher notice refrain from granting licenses for the export of reprocessing-plant technology" could actually serve to increase pressure on the government here to cancel the Brazilian sale as well.

For exanple, critics of the Brazil sale might now argue that if Bonn is acknowledging that it won't do something again, that might strengthen opponents who claim that the Brazil contract is "the wrong technology to the wrong country at the wrong time."

The West Germans made it clear once again today, however, that existing contracts "will not be affected."

Bonn has stadfastly maintained that its contract with Brazil, which has never signed the nuclear Nonproliefration Treaty, was not objected when it was first signed in 1975; that the contract has stringent safeguards to prevent misuse of nuclear material; and that Bonn's entire export economy is based heavily on faith that this country will fulfill its contracts.

The West German contract with Brazil calls for construction of nuclear power plants, which are controversial, plus plants for the richment of uranium fuel and reprocessing of spent fuel. These latter processes, though economically important for peaceful use of nuclear power, can also be directed to making atomic weapons.

The West German statement did have one important proviso, saying that Bonn is acting on the assumption that past agreements for the supply of nuclear fuel for peaceful purposes would be honored. If they are not, Bonn said, it will reconsider its new export emnargo.

What this refers to is the U.S. presure tactic used earlier this year of withholding supplies of enriched uranium fuel to West Germany to try to force cancellation of the Brazil deal. Those supplies were reinstituted in May, however, shortly before Schmid and Carter met for the first time and the London summit meeting.

At that meeting it was generally acknowleged by U.S. officials that the White House was convinced that the West Germans would not be presured out of the Brazil contract by the sudden interest of a new AmericanPresident two years after the contract was signed.

Thus, Bonn's action today could be viewed as at least a concession of sorts to U.S. efforts to control such deals in the future.

The West German statement also brings Bonn's policy publicly and formally in line with that of France, which made a similar pledge about future sales in December but has defended its right to complete existing contractwith Pakistan.